Electric switch



April 22, 1941- J. BIERENFELD ETAL ELECTRIC SWITCH Filed Aug. 24, 1936 4Sheets-Sheet 1 l/VSUL A 770 INSULATION INSULA 770M INSULA T/ ONINVENTORS. Josef ,Bz'erenfela. Afirerrc'e 6 Mace/$21922,

ATTORNEY April 22, 1941- J. BIERENFELD EIAL 2,239,031

ELECTRIC SWITCH Filed Aug. 24, 1936 4 Sheets-Sheet 2 ATTORNEY April1941- J. BIERENFELD ETAL ,2 9,031

ELECTRIC SWITCH Filed Aug. 24, 1936 4 Sheets-Sheet 3 lA/SULAT/ON INSULAT/O N 6/ INSULA T/ON lA/SULATION l V ENTORS J'ose ,Bz'e re)? fela? 1140292: re d Maeeillan.

7i ATTOR N? April 22, 1941. J. BIERENFELD ETAL ELECTRIC SWITCH 4Shets-Sheet 4 Filed Aug. 24, 1936 WEE??- Jbs an fald, LYaWrenceGMaecZZZm E ATTO R Patented Apr. 22, 1941 ELECTRIC SWITCH Josef Bierenfeld,Milwaukee, Wis., and Lawrence G. Maechtlen, Beverly Hills, CaliL,asslgnors to Square D Company, Detroit, Mich a corporation of MichiganApplication August 24, 1936, Serial No. 97,532

27 Claims.

This invention relates to electric switches, more particularly toelectro-magnetically operated switches adapted for the control ofelectric motors and other translating devices.

One object of the present invention is the provision of an electricswitch providing for ease of accessibility and replacement of the parts.

Another object of the present invention is the provision of an electric,switch having a reciprocable contact in which the contact may be readilyswung to an accessible position for inspection and replacement.

Another object of the invention is to provide an electric switch with animproved resilient mounting for the movable contacts.

Another object of the invention is to provide an electric switch with animproved stationary contact assembly permitting ready removal of thecontacts while leaving the terminals in place.

Another object of the invention is to provide an electromagneticallyoperated switch in which the magnetic structure may be readilydisassembled.

Another object of the invention is the provision of anelectromagnetically operated switch in which the movable contacts arevertically reciprocable and are hingedly mounted to be readily swungoutward for inspection and replacement.

Another object of the invention is to provide an electric switch havinga substantially enclosed arcing chamber containing separable contactswith a movable contact vertically reciprocable by connections extendingthrough the bottom of the chamber with the front of the chamber readilyremovable to permit swinging removability of the movable contacts.

Another object of the invention is to provide an electric switch with animproved form of arcing chamber.

Further objects and features of this invention will be readily apparentto those skilled in the art from the following specification and theappended drawings illustrating certain preferred embodiments of thisinvention in which:

Figure 1 is a front elevational view of an electromagnetic switchaccording to the present invention.

Figure 2 is a vertical sectional view on the line IIII of Figure l, withcertain of the parts shown in elevation.

Figure 3 is a front elevational View similar to Figure l but withcertain parts removed and the movable contact assembly swung outward asfor inspection and replacement.

Figure 4 is a horizontal sectional view through the contact chamber onthe line IV-IV of Figure 1.

Figure 5 is a perspective view of the stationary contact assembly.

Figure 6 is a horizontal sectional view on the line -VIVI of Figure 2.

Figure 7 is a horizontal sectional view on the line VII-VII of Figure 2.

The electric switch according to the present invention comprises a rearsupporting plate I upon which are mounted a plurality of contactchambers 2. Each of these chambers includes a body portion 3 secured tothe plate i by means of studs 4 and a front cover element 5 adapted toclose the chamber and maintained in position by a stud 6. Within thebody portion 3 is removably mounted a stationary contact assembly shownin perspective in Figure 5 and composed of an insulating portion 1having side projections 8 cooperating with parts within the body portion3 to position the assembly. At the front and rear of the insulating pQtion I 'are mounted contact elements 9 and H having contact faces l2 andI3 on their bottom portions. Each of these contact elements is securedto a U-shaped retaining element l4 received within suitable openings atthe top of the insulating portion 5 as by'means of studs l5 thus servingto mount the stationary contacts on the insulating portion. As shown,the contact element 9 has an integral projection l6 extending to theleft while contact element l I has a similar extension I! extending tothe right for a purpose to be hereinafter described.

At the left hand upper front corner of the base 3 is mounted aconducting connector plate l8 adapted to have a circuit terminalconnected thereto. The upper right hand portion of the base 3 isrecessed to a position slightly beyond the interior position of theextension i1. and at the back of. this recessed portion is mounted asimilar connector plate I 9 adapted to have another circuit terminalconnected thereto. When the stationary contact block is inserted in thebody portion 3 the extension It will contact with the connector plate l8and the extension I! will connect with the connector plate [9. Theseextensions and plates are conductively and mechanically connected bymeans of studs 2| and 22. The bottom of the body portion 3 at the frontthereof is provided with a slot 23 to provide entrance for the movablecontact assembly to be hereinafter described and the portion of thisslot not occupied by the mounting of the movable contact is closed byportion 24 on the cover 5.

The movable contact assembly comprises an insulating supporting block 25having mounted thereon a plurality of generally U-shaped supports 26which have their free ends bent over as at 21 to maintain a contactplate in place. Within each of the u-shaped supports 26 is mounted apair of oppositely directed interfitting U-shaped members 28 and 28 andwithin the chamber formed by the U-shaped members 26, 28 and 26 isdisposed a compression spring 3| adapted to bias the movable contactplate against the bent over portions 21. The movable contact comprises aconducting plate 32 having contact surfaces 33 and 34 at the endsthereof. The thickness of the plate 32 is less than the distance betweenthe bent over portions 21 so that the contact plate may be easilyinserted edgewise and then upon being turned flat will be pressedagainst these bent over portions by the biasing spring 3i. It is notedby this construction that the biasing spring for the movable contact ismounted within an enclosed chamber and is entirely concealed there- Asupporting bracket 35 is rigidly secured to the plate I as by means ofriveting. This bracket is of generally L-shape and is U-shaped in crosssection. At the bottom end of the bracket 35 is hingedly mounted a link36, also generally U-shaped in cross section as by means of a pivot pin31. To the link 36 is pivoted a generally U-shaped connecting link 38,also U-shaped in cross section and extending at the front of theoperating structure and rigidly secured at its upper end to theinsulating block 25 as by means of studs 39. The links 38 and 36 arepivoted together by means of pin 4land upon this pin is also pivotallymounted the armature member 42 properly positioned by means of spacers43. A spring 40 biases the back end or the armature 42 upwardly and thisrotative movement is limited by a stop 44 on the link 38.

To operate the switch there is provided a stationary magnet structureincluding a central core 45 about which is wrapped a coil 46 and whichhas connected thereto leg portions 41 at the exterior of the coil 46. Ashading coil 48 is placed at the face of each of the legs 41. Thisstationary magnet and coil assembly is mounted for ready removability.At the rear upper portion of the bracket 35 is rigidly secured a pin 49and the upper rear corner of the stationary magnet structure is providedwith a slot adapted to receive the pin 49 therein. The upper frontportion of the bracket 35 is provided with opposite openings adapted toreceive a removable pin 52 which registers with a slot 53 at the frontupper portion of the stationary magnet structure. A pair of swingingresilient arms 54 are mounted on opposite sides of the bracket 35 andserve to maintain the pin 52 in place.

On either side of the magnet structure are mounted overload relaysgenerally designated by the numeral 55. These may be of standardconstruction so far as the operation of the switch is concerned and theyhave here been shown generally and are not to be described in detail asthey form no part of thepresent invention. These relays have elementsresponsive to the current through the switch and are adapted tointerrupt the current through the magnet coil to open the switch uponthe occurrence of an overload.

The body portions 3 may be provided with integral bottom extensions 56upon which may be mounted auxiliary contacts 51 adapted to be contactedby movable switching elements 53 resiliently supported upon theinsulating block 25. These auxiliary contacts may be used for anypurpose and may constitute holding switches forthe control circuit orthe switch.

To facilitate the interruption of any are drawn between the contacts, apair of U-shaped magnetic yokes 3| substantially embracing the spacebetween the contacts when separated, are provided. The rear yoke H isrigidly secured as by riveting to the back of the interior of the bodyportion 3 and the opposite yoke 6| is rigidly secured on the-interiorrace of the cover 5 and is removable therewith.

The operation and function of the parts will now be described:

The switch as shown in Figure 2 is in the Oil! position. Upon theenergization oi the coil 41 the armature 42 will be attracted to thestationary magnet structure and through the link 38 will move the block25 vertically so as to move the contact surfaces 33 and 34 intoengagement with stationary contact surfaces l2 and I3. This completesthe circuit through the switch. Upon the de-energization of the coil 46the armature 42 will move 'away from the stationary contact structure bygravity, thus moving the contact block and associated movable contactsdownwardly to separate the movable contacts from the stationarycontacts. This reciprocatory movement of the movable contact structureis guided by the engagement of the support for the movable contact platewithin the opening formed by the back and side surfaces of the slot 23and the back surface of the portion 24 01 the cover 25.

If it is desired to inspect or replace the movable contacts 33 and 34,the covers 5 are removed as shown in Figure 3, whereupon the movablecontact assembly may b swung forwardly, entirely out of the body portion3 of the arcing chamber into the position shown in Figure 3 where thecontacts may be readily inspected and replaced. It'can be seen that thisoperation may be performed with great ease as only the studs 6 need beloosened to permit the covers to be removed and the contacts swungoutwardly.

If it is also desired to inspect and replace the stationary contactsthis requires only the removal of the studs 2| and 22 whereupon theentire stationary contact assembly may be removed from the switchstructure. The contact elements 9 and II can themselves be readilyremoved from the insulating portion I by the removal of the studs l5. Inthe arcing chamber shown at the upper right hand corner of Figure 3 thestationary contact block has been removed. Toremove any one stationarycontact block it is necessary only to remove the associated cover 5 andit is not necessary to remove the other covers or to swing the movablecontact assembly outward.

If it is desired to replace the stationary magnet structure or toreplace a magnet coil the movable contact assembly is swung outwardly asheretofore described and as shown in Figure 3 and the spring arms 54 aremoved out of engagement with the pin 52. Upon removal of this pin 52 thestationary magnet structure and coil may be entirely removed from theswitch. To replace a magnet structure after removal the slot 5! is againengaged with the pin 49, the pin 52 is inserted through the openings inbracket 35 into engagement with the grooves 53 and the spring arms 54are moved into engagement with the pin 52.

In connection with the removal oi the staaaaaosr tionary contactassembly it is to be noted that this is effected without detachment ofthe circult terminals as these are connected to the ter- .minal platesis and I! which remain in place when the contact block is removed, thusgreatly reducing the time and trouble in removing the stationarycontacts.

While the body portions of the contact chambers may obviously be joinedto form compartments in a single block and/or a single elongated covermay be used, with the chambers divided as herein disclosed greaterflexibility is secured in building up any desired number of poles wherevariations are required.

While certain preferred embodiments of the invention have beenspecifically disclosed, it is understood that the invention is notlimited thereto as many variations will be readily apparent to thoseskilled in the art and the invention is to be given its broadestinterpretation within the terms of the following claims.

What is claimed is:

1. In an electric switch, an insulating arc enclosing and suppressingchamber having an openable front, a stationary contact assembly withinsaid chamber and comprising an insulating block having a pair ofstationary contacts mounted thereon, a bridging movable contact withinsaid chamber having supporting means extending through the bottom of thechamber for reciprocating said movable contact into and out ofengagement with said stationary contacts, electromagnetic means foreifecting reciprocation of said movable contact, and a removable frontcover for said chamber providing forready forward removability of thestationary contact assembly and for supported swinging removability ofsaid movable contact when the front cover is removed.

2. In an electromagnetically operated electric switch an insulating arcenclosing and suppressing chamber composed of relatively fixed andrelatively removable portions, a terminal connector mounted at theexterior on a rela-,

tion of the circuit wire to the terminal connector.

3. In an electromagnetically operated electric switch an insulating arcenclosing and suppressing chamber formed of relatively fixed andrelatively removable portions, a terminal connector mounted at theexterior on a relatively flxed portion of said chamber and adapted tohave a circuit wire connected thereto, a stationary contact within saidchamber mounted on a relatively removable portion thereof, a movablecontact within said chamber, means at the exterior of said chamber formoving the movable contact into and out of engagement with thestationary contact to perform the switching operation, and

a readily releasable connection between said stationary contact and saidterminal connector whereby said stationary contact and the removableportion of the chamber upon which it is mounted may be readily removedfor inspection or replacement without disturbing the circuit wireconnection to the terminal connector.

4. In an electromagnetically operated electric switch an insulating arcenclosing and suppressing chamber formed of relatively fixed andremovable sections, terminal connectors mounted at the exterior on arelatively fixed portion of said chamber and adapted to have circuitwires connected thereto, spaced stationary contacts within said chamberand mounted on a relatively removable portion thereof, a movable contactwithin said chamber adapted to bridge said stationary contacts, means atthe exterior of said chamber for vertically reciprocating said movablecontact into and onto! engagement with the stationary contacts toperform the switching operation, and readily releasable connectionsbetween said stationary contacts and said terminal connectors wherebythe stationary contacts and removable portions ofthe chamber upon whichthey are mounted may be readily removed without disturbing the terminalconnector and the circuit wires connected thereto.

5. In an elcctromagnetically operated electric switch, spaced stationarycontacts, a movable contact rectilineariy movable in a vertical planeinto and out of bridging relation with said stationary contacts toeffect the switching operation, a stationary magnet structure below saidstationary and movable contacts, an armature member below saidstationary magnet structure and adapted to be attracted into engagementtherewith, and a power transmitting member connected to said armatureand to the movable contact and extending in front of said stationarymagnet structure, said last mentioned member being nmnually swingableforwardly of the switch to expose the movable contact and to provideaccess to the stationary magnet structure.

6. In an electromagnetically operated electric switch, a stationarycontact, a movable contact, means biasing said movable contact todisengaged position, electromagnetic means for moving said movablecontact into engaged position, guide means normally limiting movement ofsaid movablev contact to a straight line rectilinear movement inresponse to energization and deenergization of saidelectromagneticmeans, and means providing for manual swinging movement of themovablecontact into a readilyaccessible position for manipulation.

7. In an electromagnetically operated, electric switch, a sectionalarcing chamber having at least a bottom opening therein, stationary andmovable contacts within said chamber, electromagnetic means below saidchamber, means connecting said electromagnetic means to said movablecontact and extending through said bottom opening, said movable contactbeing normally guided'for rectilinear movement by the walls of saidopening in response to energization and deenergization of saidelectromagnetic means, said chamber including a front portion readilyremovably mounted to remove the front boundary wall for said bottomopening, and means providing for manual swinging movement ofd movablecontact out of said chamber and into readily accessible position whensaid front chamber portion is removed.

8. In an electroma netically operated electric switch, spaced stationarycontacts, a movable contact plate for bridging said stationary contactsto perform the switching operation, an electromagnetic operator, meansconnecting said movable contact plate to said electromagnetic forming afront wall for the bottom opening, a

stationary contact within said chamber, a movable contactwithin saidchamber, an electromagnetic operator beneath said chamber, meansconnecting said electromagnetic operator to said movable contact andextending through said bottom opening and guided thereby for rectilinearmovement in response to energization and deenergization of saidelectromagnetic operator, and means providing for swinging movement ofsaid movable contact forwardly into a readily accessible position afterremoval of said front cover.

10. In an electromagnetically operated electric switch, a plurality ofside by side arcing chambers having open fronts andopenings in theirbottoms extending to the front, cover means for said chambers includingsurfaces providing front walls for said bottom openings, stationarycontacts within said chambers, movable contacts within said chambers,means extending through said bottom openings and carrying said movablecontacts and normally guided for straight line rectilinear movement,beneath said chamber and connected to said contact carrying means foreffecting movement thereof, and means providing for swinging movement ofthe movable contacts forwardly into a readily accessible position uponremoval of said front cover.

11. In an electromagnetically operated electric switch, a stationarycontact, a movable contact normally rectilinearly movable into and outof engagement with said stationary contact, a rigid link pivoted to afixed part, a force transmitting member pivoted to the free end of saidlink and having an operative connection with said movable contact, anarmature element operatively connected to effect movement of the pivotalconnection between said member and link, means for attracting andreleasing said' armature to effect the switching operation, and meansguiding a part movable with the movable contact so as to limit it tonormal rectilinear movement in response to movement of the armature,atleast a part of said last mentioned means being readily removable toprovide for manual swinging movement of the movable contact about thepivots of said member and link into a readily accessible position.

12. In an electromagnetically operated electric switch, a stationarycontact, a movable contact normally rectilinearly movable into and outof engagement with said stationary contact, an operating electromagnet,pivotally mounted and connected linkage means having an operativeconnection with said movable contact, an armature connected to saidlinkage means to effect movement thereof in response to energization anddeenerg'ization of said operating electromagnet, and means guiding apart movable with the movable contact so as to limit it to normalrectilinear electromagnetic means movement in response to movement ofsaid linkage by movement of said armature to effect the switchingoperation, at least a part of said last mentioned means being removableto provide for manual swinging movement of the movable contact about thepivots of said linkage into a readily accessible position formanipulation.

13. In an electromagnetically operated electric switch, a stationarycontact, a movable contact, electromagnetic means normally operating toeffect rectilinear reciprocatory movement of the movable contact intoand out of engagement with the stationary contact in response toenergization and deenergization of the electromagnetic means to performthe switching operation, and means providing for manual swingingmovement of said movable contact into a readily accessible positionremote from its normal path of movement and from said stationarycontact, whereby the movable contact may be readily inspected andmanipulation thereof facilitated.

14. In an electromagnetically operated electric switch, an arcingchamber, stationary and movable contacts, within said chamber,electromagnetic means exterior of said chamber normally operating toeffect rectilinear reciprocatory movement of the movable contact withinthe chamber into and out of engagement with the stationary contact inresponse to energiaation and deenergization of the electromagnetic meansto perform the switching operation, and means providing for manualswinging movement of said movable contact out of said chamber and into areadily accessible position at the exterior thereof, and remote from itsnormal path of movement and from said stationary contact, whereby themovable contact may be readily inspected and manipulation thereoffacilitated.

15. In an electromagnetically operated electric switch, spacedstationary contacts, a movable contact plate normally rectilinearlymovable into and out of bridging relation with said stationary contacts,electromagnetic means normally operating to effect rectilinearreciprocatory movement of said movable contact plate in response toenergization and deenergization of the electromagnetic means to performthe switching operation, and means provided for manual swinging movementof said movable contact plate into a readily accessible position remotefrom its normal path of movement and from said stationary contacts,whereby the contact plate may be readily inspected and manipulationthereof facilitated.

16. In an electromagnetically operated electric switch an arc chamberhaving an open front and an opening in its bottom extending to thefront, a stationary contact within said chamber, a movable contactwithin said chamber adapted to be normally rcciprocated therein into andout of engagement with the stationary contact, a front cover for saidchamber closing said front opening but maintaining the bottom openinginto said chamber, operating means extending through said bottom openinginto said chamber and carrying said movable contact, electromagneticmeans at the exterior of and beneath said chamher and connected to saidoperating means to effect rectilinear reciprocatory movement thereof inresponse to energization and deenergization' hithe electromagnetic meansto perform the switching operation, and means providing for manualswinging movement of said movable contact out of said chamber whensaid'front cover is removed, and into a readily accessible positionremote from its normal path of movement andfrom said stationary contact,whereby the movable contact may be readily inspected and manipulationthereof facilitated.

17. In an electromagnetically operated electric switch, stationary andmovable contacts, pivotally mounted supporting means for said movablecontact, means normally guiding said movable contact for substantiallyrectilinear movement only,

'of movement and from said stationary contact,

whereby the movable contact may be readily inspected and manipulationthereof facilitated.

18. In an electromagnetically operated electric switch for industrialcontrol service, stationary and movable contacts, a link connected tosaid movable contact, a second link pivoted into said first link into afixed part, an armature pivotally mounted on said links, a stationarymagnet structure for attracting and releasing said armature in responseto energization and deenergization thereof and operated to effectmovement of said armature and of the pivotal connection between saidlinks in a direction substantially parallel to the direction of normalmovement of the movable contacts, and means guiding said movable contactfor substantially rectilinear movement only in response to movement ofsaid armature toward and away from the said magnet structure.

19. In an electromagnetically operated electric switch for industrialcontrol service, stationary and movable contacts, a pivotally mountedlink connected to said movable contact, an armature connected to saidlink, a stationary magnet structure operating to attract and releasesaid armature in response to energization and deenergiza- -tion of themagnet structure to perform the switching operation whereby the movablecontact is moved into and out of engagement with the stationary contact,means for guiding said movable contact for normal substantially verticalrectilinear movement in response to such movement of said armature, atleast a portion of said guiding means being removable to provide formanual swinging movement of the movable contact into a readilyaccessible position remote from its normal path of movement and fromsaid stationary contact, whereby the movablecontact may be readilyinspected and manipulation thereof facilitated.

20. In an electromagnetically operated electric switch for industrialcontrol service, a stationary. contact, a reciprocable member, a movablecontact connected to said member to be moved thereby into and out ofengagement with the stationary contact, a link pivoted to said memberand to a fixed part, an armature pivotally mounted on said link andmember, and a stationary magnet structure for attracting and releasingsaid armature in response to energize.- tion and deenergization thereof,and operating to eiIect movement of'the pivotal connection between saidlink and member in a direction substantially parallel to the directionof movement of said movable contact, and guiding means for normallylimiting movement of said reciprocable member to a substantiallystraight line of rectilinear movement only.

21. In an electromagnetically operated electric switch, an arcingchamber having an openable front cover and an opening in the bottomthereof extending to said cover, stationary and movable contacts withinsaid chamber, a support for said movable contact projecting through saidbottom opening, electromagnetic means at the exterior of and beneathsaid chamber normally operating to efiect rectilinear reciprocatorymovement of the movable contact within the chamber into and out ofengagement with the stationary contact in response to energization anddeenergization of the electromagnetic means to perform the switchingoperation, and means providing for manual swinging movement of saidmovable contact out of said chamber when said front cover is open andinto a readily accessible position at the exterior of the chamber remotefrom its normal path of movement and from said stationary contact,whereby the movable contact may be readily inspected and manipulationthereof facilitated. a

22. In an electromagnetically operated electric switch, spacedstationary contacts, a movable contact plate adapted to be moved intoand out of bridging relation with said stationary contacts, aninsulating body portion having an openable front cover and substantiallyenclosing said contacts and contact plate except for an entrance openingthrough which extends the supporting and manipulating means for themovable contact, electromagnetic means at the exterior of and beneathsaid body portion normally operating to eifect rectilinear reciprocatorymovement of the movable contact into and out of engagement with thestationary contacts in response to energization and deenergization ofthe electromagnetic means to perform the switching operation, the frontcover of the insulating body portion being readily manually openable toprovide for readily manual removal of said stationary contacts and forsupporting swinging removal of said movable contact plate out of saidbody portion and into a readily accessible position at the exteriorthereof remote from its normal path of movement and said stationarycontact, whereby the contact plate may be readily inspected andmanipulation thereof facilitated.

23. In an electromagnetically operated electric switch, spacedstationary contacts, a movable contact plate adapted to be movable intoand out of bridging relation with said stationary contacts, a chambersubstantially enclosing said contacts, electromagnetic means at theexterior of said chamber normally operating to effect rectilinearreciprocatory movement of the movable contact plate within the chamberinto and out of engagement with stationary contacts in response toenergization and deenergization of the electromagnetic means to performthe switching operation, a pair of oppositely directed U-shaped magneticyokes within said chamber, each of said yokes being disposed with itslegs on opposite sides of one of said stationary contacts and with itsbight outside of the path of movement of the movable contact plate withthe plane of the U disposed substantially at right angles to the path ofmovement of the movable contact plate.

24. In an electromagnetically operated electric switch, spacedstationary contacts, a movable contact plate adapted to be moved intoand out chamber normally operating to eifect rectilinear reciprocatorymovement of the movable contact plate within the chamber into and out orengagement with stationary contacts in response to energization anddeenergization of the electromagnetic means to perform the switchingoperation, and a pair of U-shaped magnetic yokes disposed in saidchamber with their legs spaced from, but embracing at least a portion01', the path of the movable contact adjacent to the stationary contactsand with the plane oi the U disposed at substantially right angles tothe direction of said path.

25. In an electric switch, a contact chamber having an openable frontcover, stationary contacts within said chamber and spaced longitudinallythereof, a movable contact within said chamber adapted to bridge saidstationary contacts, means for moving said movable contact within saidchamber into and out of engagement withsaid stationary contacts, aU-shaped magnetic yoke mounted on the back interior wall of said chamberand embracing the path of contact movement adjacent to the backstationary contact and a second U-shaped magnetic yoke mounted-on theinterior wall of the cover and embracing the path of contact movementadjacent to the front stationary contact when said cover is in place.

26. In an electric switch, a contact chamber, a

, stationary contact assembly in said chamber comprising a removableinsulating block and a pair of spaced contacts associated with saidblock, terminal members mounted on a stationary portion of said chamberand having means I I a,

thereon for the reception of circuit wires, means for connecting saidstationary contacts to said terminal members so as to be rigidlysupported therefrom independent of their association with the removableinsulating block, said connecting means being readily disconnected andproviding for removal of the insulating block and the stationarycontacts as a unit assembly while said terminal members remain mountedon the stationary portion of the contact chamber, whereby removal of thestationary contacts as a unit may be readily effected without disturbingthe circuit wiring connections.

27. In an electric switch, a contact chamber formed of front and backinsulating elements, means mounting said back insulating element on asupport, means removably mounting said front insulating element incooperating relation with the back insulating elements, terminal membersrigidly mounted on the back insulating element and having means'for theattachment of circuit wires, a stationary contact assembly in saidchamber comprising a removable insulating block and a pair of spacedcontacts associated therewith, means connecting said contacts to saidterminals so as to be rigidly supported therefrom independent of theirassociation with the removable insulating block, said connectin meansbeing readily disconnected and providing for removal of the insulatingblock and contacts as a unit assembly while said terminal members remainmounted on the back insulating element, whereby removal of the contactsas a unit may be readily effected without disturbing the circuit wiringconnections.

JOSEF BIERENFELD. LAWRENCE G. MAECH'I'LEN.

